The present invention relates, generally, to ignition systems for portable power tools and, in particular, to ignition systems that include an ignition switch, choke mechanism and air filter unit.
Portable power tools such as chain saws, hedge trimmers, edgers and blowers, typically, are powered by a gasoline engine the operation of which is controlled by an ignition switch. The ignition switch is manually movable between an “On” position allowing the engine to operate and an “Off” position preventing the engine from operating. Usually, these power tools are also provided with a manually controlled choke mechanism to facilitate the starting and running of the gasoline engine. The engine requires both fuel and air to operate and, by manipulating the choke mechanism, the relative quantities of air and fuel delivered to the engine are varied so that the engine can be readily started and, thereafter, operated. For example, if the engine has been idle for a period of time and the ambient temperature is relatively low, in order to start the engine, it is necessary that an air-fuel mixture that is rich in fuel be delivered to the engine with the ignition switch in the “On” position. To produce a fuel-rich air-fuel mixture the choke mechanism is adjusted so that it restricts the intake of air to the engine. Once the engine has started, the choke mechanism is adjusted once again so that the quantity of air, in relation to the quantity of fuel delivered to the engine, is increased until a ratio of air to fuel is attained that allows for optimum operation of the engine. At such time as it is desired to discontinue operating the power tool, the ignition switch is moved to the “Off” position.
The air and fuel are mixed in the engine's carburetor before being delivered to the engine and, typically, the choke mechanism controls the position of a valve in the flow path of the air to the carburetor so as to control the quantity of air entering the carburetor. Because it is important to the efficient operation of the engine that the air be as free of particulate matter as possible, the air is passed through an air filter unit before it is introduced into the carburetor.